How often or how many miles can you go without replacing the fuel filter? I put all new stuff in the tank and cleaned the tank with acid to like new condition 6000 miles ago (about a year and a half ago) and wonering if it's time to change the filter.There is nothing wrong with the way the bike runs for the most part but the other day I really got on it and at about 5500 rpm it started to act funny. Slowed down and everything was good again  so I'm thinking it might be that time.Anyone?

6000 miles is about 120 gallons of gas. 

When you consider that a lot of automobiles can go 150,000+ miles which uses about 5,000 gallons running the same gas through similar filters you have to wonder how often you really need to change that filter.

That's a good point  So I guess I should look at something else as the cause of crappy high speed performance like corrosion on some connection or leaking vacuum lines

I replace whenever neccesary, most when I just buy another K.

I last replaced mine about 60,000 miles ago, just when I bought the bike.

Thanks guys . Now I am pointed in the right direction and I will start going over the hoses and connections.

Easy test.  Pull the fuel filter and try to blow through it.  It should be pretty easy.

Napa 3032 filter is readily available in the US and only about $5.

Miles/gallons aren't the only thing that mess up fuel filters. If a decent amount of water sits in a fuel filter it can swell the fibers and restrict flow.

E5 and E10 is hydroscopic, means it attracts water, like brakefluid.
And that crap gets old much faster than the old fuel, can make a mess in the filter.

Last year in Germany, I was able to take Supreme fuel 102, made a smooth racing bike of the old K

Have you checked the valve clearance?  Tight valves can make it break up.  A bad plug or plug wire can cause problems a well.  How is the air filter?

Thanks TWB, mistype in the morning

Arlina wrote:Thanks TWB, mistype in the morning

No worries, Arlina. That's what comes from having a schoolteacher for a father.

Water causes much different problems in gas vs. brake fluid.  The problem with old brake fluid that's absorbed water is that water is more compressible than brake fluid which is why brakes with old fluid get mushy.

Water in gas causes different problems.

duck wrote:Water in gas causes different problems.

No kidding?

Water is compressible?  I've never heard that before.
I thought the problem with water in brake fluid is it's tendency to boil at high temperatures, passing to a gas state, which would compress.

Yes, water is more compressible than brake fluid. Brakes with water in them will be mushy at room temperature.

And the boiling point is an issue as well.

Rust caused by water in brake components can also be an issue.

What about verdigris?

brickrider2 wrote:Water is compressible?  I've never heard that before.
I thought the problem with water in brake fluid is it's tendency to boil at high temperatures, passing to a gas state, which would compress.

Yes this is correct.
Though it is true that water is not 100% in-compressible (nothing is), water in liquid state is still considered high in density and not necessarily more compressible than brake fluid. 

The 4 critical purposes a brake fluid has to fulfil :
1. Maintain a high boiling point
2. Maintain a specific viscosity range
3. Prevent corrosion
4. Maintain low compressibility

In addition, the brake fluid must maintain [pretty much] the same compressibility across a wide temperature range, say from freezing to way above boiling temperatures. 

Water obviously does not do that, as it changes states from solid via liquid to gas and therefore also moves the values of both compressibilty and viscosity in the process.

Mixing just a tiny bit of water into the brake fluid will hence impact all of the above parameters preventing the brake fluid from fulfilling its purpose.
3% water is apparently the critical limit for brake fluid.

Best regards,
Einar

Its not difficult in mountain, very hot or racing conditions to get brakes extremely hot. Brake fluid will have a decent boiling temperature, water does not and will become steam which will of course be compressible and result in brake failure. It does not have to reach 100c for these things to happen,

Regarding the original question, when to change fuel filter I would day unless you encounter regularly low quality fuel the general recommendation is to change every 40 000 km.